The rollercoaster has gpe because it has potential to fall down once it is at the top of the ride. And once it falls from the top of the ride it will have potential energy. At point 2 it is increasing because it is falling so speed is faster. And at point 3 it is decreasing because rollercoaster is slowing down.
Next at point four it is decreasing even more because it is going upside down wich slows it down.
Next at point four it is decreasing even more because it is going upside down wich slows it down.